Boiler feed pump arrangement for steam turbine powerplant



Dec. 29, 1964 A. w. RANKIN 3,163,009

EOILEE FEED PUMP ARRANGEMENT FOR STEAM TUEEINE PowERPLANT Filed Aug. 29, 1965 2 Sheets-Sheet 2 56.2, 00%- /z' %72f7 /ia l l I l l l 0 20 40 60 80 /00 /20 /40 PER CENT FRATED FLOW [N VENTO@ ANDREW W RANK/N BY M w- 95.@

H/S A TToH/VEY United States Patent Oiice 3,163,009 Patented Dec. 2g, 1964 3,163,699 BOELER FEED PUMP ARR TGEMENT FR SEAM PWERPLANT Andrew W. Rankin, Leominster, Mass., assigner to Geueral Eieetric Company, a corporation of New York Filed Aug, 29, i963, Ser. N i. 3il5,?-fi9 6 Ciaims. (Cl, eti-97) This invention relates to steam turbine powerplants, particularly to an improved boiler feed pump arrangement. While not necessarily limited thereto, it is particularly applicable to turbines driving a load device such as an electric generator at substantially constant speed.

Various arrangements have been proposed for driving the boiler feed pump or pumps supplying condensate from the condenser to the steam generator of turbine powerplants. A commonly used expedient is to drive a single boiler feed pump by a separate prime mover, such as a variable speed electric motor or an auxiliary steam turbine. Recently it has become increasingly common to drive the boiler feed pump directly from the shaft of the main steam turbine, by means of an appropriate variable speed drive such as a hydraulic coupling. Such variable speed drives represent a substantial investment in equipment, and cost the powerplant a signiiicant amount of energy due to the losses inherent in the hydraulic coupling.

Accordingly, -a primary object of the present invention is to provide an improved combination-drive boiler feed pump arrangement giving better overall thermal efiiciency by elimination of the losses in the variable speed drive, and at the same time reducing the initial cost of the equipment.

Another object is to provide a boiler feed pump arrangement for a steam turbine powerplant having a high degree of reliability, by providing a combination of two feed pumps, either of which is capable of supporting the operation of the powerplant at reduced load.

A still further object is to provide an improved feed pump arrangement making possible an improved method for starting the plant.

Still another object is to provide a combination boiler feed pump arrangement which eliminates the necessity for a separate motor-driven feed pump for starting the plant.

Other objects and advantages will become apparent from the following description, taken in connection with the accompanying drawing, in which FIG. 1 represents diagrammatically a steam turbine powerplant incorporating the invention, FIG. 2 is a diagrammatic representation of the interrelation of the operation of the various conltrol devices of FIG. l, and FIG. 3 represents the operating characteristics of one of the boilerfeed pumps employed.

General Description,

the flow from the main shaft driven pump, to provide the feedwater iiow rate required.

Referring now more particularly to the drawing, the invention is illustrated as applied to a steam turbine power-plant comprising a main boiler or steam generator 1 supplying motive uid to a main turbine 2 driving a constant speed load device, illustrated as being a generator 3. Turbine 2 exhausts to a condenser 4, and the main boiler is supplied with feedwater by a pair of feed pumps. The rst pump 5 is directly connected to the shaft of the main turbine 2, and theA second pump 6 is driven by an auxiliary steam turbine -7, pumps 5, vti being connecte in parallel to supply the main boiler l. Y

in accordance with the invention, the main shaft-driven feed pump 5 is provided with a discharge regulating valve 8, under the control of an integrating feedwater control device li, the function of which is to regulate the feedwater flow rate by appropriately adjusting the valve 8 and the throttle vaive gear 7e (and 7h) of auxiliary turbine 7. Turbine 7 is supplied with motive iiuid either from an extraction port 2a in the main turbine 2, or from an auxiliary package steam generator 9, or from an external source of steam represented by supply conduit l0, or direct from the main boiler 1 by a bypass conduit 1d.

The piping and valves required for the interconnection and control of these components are more completely described as follows:

The main boiler 1 supplies steam by way of a superheater la past a check valve 1b to the valve gear of the main turbine 2, comprising an emergency stop valve 2b and the turbine throttle valve gear 2c, the details of which need not be described here, since purely conventional. Turbine 2 exhausts to the condenser 4 by way of conduit 2d.

in normal operation, the auxiliary boiler feed pump turbine 7 will be supplied with motive iluid by an extraction conduit 7a from the intermediate pressure extraction port 2a of the main turbine 2, by Way of a check valve 7b, valve 7c, emergency stop valve "7d, and the turbine throttle gear 7e. The external steam supply conduit 10 is provided with a valve 10a. Auxiliary steam generator 9 may supply motive fluid to the turbine 7 -by way of a conduit 9a provided with a valve9b communicating with the auxiliary turbine supply conduit 7a upstream from the emergency stop valve 7d. The -auxiliary turbine 7 may also be supplied with steam from the-main -high pressure supply conduit lc by way of a bypass conduit ia' containing a shut-off valve le, emergency stop Valve 7g, and throttle valve 7h. The auxiliary boiler l9 ,may also supply steam for starting the main turbine 2 by way of a conduit 9c containing a Avalve 9d, by way -of conduits 1d, lc. Auxiliary turbine 7 may of course `exhaust to condenser 4, or to some appropriate processrequiring steam for heating or other purposes.

The piping for the boiler feed pumps 5,26 includes conduit 4a furnishing condensate from condenser 4 1in parallel to the two feed pumps, by way of valves-f4b, 44C. The main shaft driven feed pump Svdelivers its output by way of conduit 5a containing the special regulating valve 8 and a check valve 5b. The other feed pump 6 delivers its output byway of conduit tia containing a shut-off valve 6b and check valve 6c. It will beapparent that pumps 5, 6 are thus arranged in parallel to supply feedwater to the main boiler ll by way of conduit 1f.

The boiler feed pumps b', d are regulated by an inteaisance grating type feedwater controlrer 11 which receives several condition-responsive input signals and puts out a single integrated control signal, which is furnished as indicated by dotted line 11a to a relay 8a connected to control the feedwater throttling valve 8, and by way of line 11b to a speed-setting relay 'if connected to control the throttle valve gear 7e, '7h of the auxiliary turbine '7. The input signals to feedwater controller 11 may include, among others, the level of the Water in the steam drum 1g of the boiler 1, represented by dotted line 11e, the rate of flow of steam supplied by boiler 1, indicated by line 11d to flowmeter 11e, and the rate of feedwater supply to the boiler, indicated by line 11f connected to flowmeter 11g.

The details of the feedwater controller 11 are not described here since this is a standard article of commerce, and may for instance be similar to that manufactured by the Bailey Meter Company and designated as 3-Element Control System.

Operation The versatility of this feed pump arrangement wili be seen from the following description of the various modes of operation. In FIG. 1, solid arrows indicate flow in normal operation, while dotted arrows indicate iiow under special operating conditions. Dotted lines indicate conv trol signal conduits or circuits.

In normal operation, the main turbine 2 operates at constant speed as required by the electric generator 3, so that the speed of the direct-connected feed pump 5 is also constant. Accordingly, pump 5 operates according to the characteristics illustrated in FIG. 3. At full load,

the second feed pump 6 is also driven at the same rated speed by the auxiliary turbine 7, its motive uid ordinarily being supplied from the extract port 2a of the main turbine Z.

For operation below normal rated load, the feed pump 5 continues to operate at rated speed, and the feedwater controller 11 causes relay 7f and valve gear 7e to reduce the speed of the auxiliary turbine 7 so that the feed pump 6 operating in parallel with pump y5 furnishes the total Y flow rate to satisfy the requirements of controller 11. Decreasing load on turbine 2 is of course accompanied by closing of the throttle valve gear 2c, which reduces the flow rate demanded from the boiler 1. Thereupon the controller 11 acts to close the auxiliary turbine throttle valve gear,7e. Thus, as the load on turbine 2 falls, the valve gear 7e reduces the speed of the auxiliary turbine 7.

' At approximately 65% of normal rated load, the auxiliary turbine valve 7e is completely closed and the boiler feed pump 6 is inactive, reverse ilow through the conduit 6a being prevented by the check valve 6c.y Thus, at and below 65% load, the iirst boiler feed pump 5 supplies the entire feed water requirements of the main steam boiler 1.

regulating valve 8 is rarely called upon to perform its throttling function.

` The mechanical details of the relays 7i, 8a are not shown because these are standard items which may take many forms. For instance, the feedwater control valve 8 and relay 8a may be combined as a type VL class D10 valve as sold by the Bailey Meter Company. Numerous types of hydraulic regulators or electric governors may be used at 7] to control turbine 7.

FIG. 2 is a nomograph illustrating the interrelation between the operation of the feedwater controller 11, the feedwater throttling relay 8a, the auxiliary turbine control relay 7f, and the respective valves 8, 7e (or 7h) controlled thereby.

In the upper part of the diagram, the scale on ordinate 12 represents the magnitude of the integrated signal put out by the feedwater controller 11. The diagram in the lower left corner of FiG. 2 includes an abscissa 13 representing the degree of opening of the feedwater throttling valve 8. in the lower right corner, the diagram has an abscissa 14 indicating the degree of opening of the auxiliary turbine control valve gear 7e. The lower mid-portion of FIG. 2 includes the construction line 15 representing the action of the feedwater throttling relay 8a, while the construction line 16 represents the effect of the auxiliary turbine control relay 7).

The manner of reading FlG. 2 to determine the integrated operation of the control system will be seen from the following.

At zero feedwater signal on the scale 12, the dotted horizontal line 13b and vertical ordinate 13e indicates on scale 13 that the feedwater valve S is closed. Likewise the dotted horizontal line 1417 and vertical ordinate 14C indicates on the scale 1.4 that the auxiliary turbine control valve '7e is also closed.

Suppose now that the feedwater control signal from the device 11 rises to a value of 40% of its maximum value. Then the horizontal dotted line 12b intersecting the construction line 12a, the vertical dotted line 15a intersecting the construction line 15, the horizontal dotted line 13a! intersecting the construction line 13a, and the vertical dotted line 13e indicates on the abscissa scale 13 that the feedwater valve 8 is at 60% of its maximum open position.

When the feedwater control signal on scale 12 rises to the 65% transition point, the horizontal dashed line 12C, the vertical dashed line 12d, the horizontal dotted line 131 and the vertical dotted line 13g indicate on the feedwater valve scale 13 that the valve 8 is in its 100% open position. Similarly, the dashed line 12a intersecting the construction line 16, the horizontal dotted line 1Gb, and the ordinate 14C indicate that the auxiliary turbine valve '7e is still closed.

If now the feedwater control signal on scale 12 rises to the level, then the horizontal line 12e intersecting construction line 12a, vertical dotted line 16a intersecting the construction line 16, the horizontal dotted line 14d intersecting the construction line 14n, and the vertical dotted line 14e indicate on the abscissa scale 14 that the auxiliary turbine valve 7e is 60% open.

The horizontal portion 15b of the construction line 15, representing the action of relay 8a, indicates that the feedwater valve 8 is held in wide open position throughout the range where the relay 7j is in control.

At on feedwater signal scale 12, the dashed line 12j, vertical dashed line 12g, horizontal dotted line 141, and vertical dotted line 14g indicate that the auxiliary valve 7e is wide open.

It is to be noted that the performance characteristics represented by FIG. 2 do not represent any particular operating system, but are merely for the purpose of illustrating the manner of reading FIG. 2, The actual slope and shape of the construction lines in FIG. 2 will be dependent on the operating characteristics of the specific types of controller 11, relays 7j, 8a and valves 7e, 7h, S, etc. employed.

The principal function of the auxiliary boiler 9 is to provide motive fluid for the auxiliary turbine 7 in starting the powerplant. To this end, the shutoif valve 9b would be opened and steam supplied by way of conduit 9a, emergency stop valve '7d and valve gear 7e to drive turbine 'i so that the pump 6 supplies the feedwater required to start the main boiler 1. With the main boiler 1 in operation, the turbine 2 can be brought up to rated speed and the generator 3 connected to its distribution network (not shown). As the speed of pump 5 rises, the feedwater controller 11 will close the auxiliary turbine valve gear 7e, and the auxiliary boiler 9 can be shut down and valve 9b closed (after valve 7c is first opened to admit motive fluid to conduit 7a from the extraction port 2a of main turbine 2). As the load on turbine 2 rises to the 65% level, the regulating valves S will be opened wide, and above that point controller 11 will cause the valve gear 7e to open again so auxiliary turbine 7 increases in speed.

An additional advantage of having the auxiliary steam supply 10 and the auxiliary package boiler 9 is that they furnish means for increasing the maximum capability of the main turbine 2. That is, the valve 7c may be closed to stop the supply of extraction steam from the main turbine 2, so that auxiliary turbine 7 is driven entirely by the auxiliary boiler 9 (or separate steam supply 1G), thus increasing the power output of the main turbine 2 available for driving generator 3 for peak load operation. Thus the arrangement provides an economical way to get additional peaking capacity. For such eaking operation, auxiliary turbine 7 may alternatively be supplied with motive iiuid from the main boiler 1 by opening valves 1e, 7g in the bypass conduit 1d, turbine '7 then being regulated by valve gear 7h, under control of relay 77.

Another advantage of this improved arrangement is that either feed pump may be taken out of operation and the plant operated at a fraction of its normal rated output. Such operation may be accomplished as follows.

Assume rst that it is desired to take the main shaftdriven pump 5 out of operation. This is accomplished by manually closing the regulating valve 8 and the shutoff valve 4b, so that pump 5 can be removed for servicing. The plant would then be started as described above by operating the auxiliary steam generator 9 to drive the auxiliary turbine 7, and when the main boiler 1 is in operation, the auxiliary turbine 7 can be supplied with steam from the extraction port 2a and the auxiliary boiler 9 shut down. Under such circumstances, the total output of the plant would be limited to perhaps 65% of normal rated load.

Conversely, the second boiler feed pump 6 may be removed from the circuit by closing the shutoff valves 4c, 6b. The plant would now be started by supplying steam to main turbine 2 from the auxiliary inlet 10 or the auxiliary boiler 9 by way of conduit 9c, by opening valve 9d, so that steam is supplied by way of conduits 1d and 1c to turbine 2. Operation of the main turbine provides boiler feedwater from the pump 5, the load again being limited to some fraction of normal rated load. The valve 9d would of course be closed and the auxiliary boiler 9 shut down as soon as the main boiler 1 is in normal operation.

Conclusion It will be seen that this improved boiler feed pump arrangement permits taking either feed pump out of the circuit for servicing while still using the plant at part load.

The over-all availability and reliability of the plant is thus improved.

The auxiliary turbine 7 with its secondary sources of motive uid also provides a convenient method of starting the plant, without requiring the entirely separate motor-driven start-up pump heretofore necessary. The improved thermal efficiency of the plant is partly due to the fact that auxiliary steam turbine 7 maintains its eflciency at reduced speeds better than either a variable speed electric motor or a variable speed hydraulic coupling as heretofore used. The elimination of the separate start-up pump substantially reduces the first cost of the equipment.

Thus it will be seen that the invention provides a substantially improved boiler feed pump arrangement having lower lirst cost, better thermal efficiency, and improved reliability, as compared with those heretofore employed.

While only one specific embodiment has been described, it will be apparent that numerous modifications may be made. For instance, instead of completely shutting down the auxiliary turbine 7 at part load, it may continue to be supplied with a limited quantity of steam to keep it rotating at some desired minimum speed, the water discharged from the feed pump 6 being recirculated to the condenser, so that a certain minimum circulation through the pump 6 is effected to prevent overheating of the pump. It will also be obvious that other means for controlling the turbine 7 and regulating valve 8 may be employed, in place of the specified controller 11 and relays 71, 8a.

While the economies,-both in rst cost of the equipment and in overall thermal eiciency, are best achieved by completely eliminating the hydraulic coupling between the main turbine 2 and feedwater pump 5, there may in some installations be extraneous reasons for wanting a' hydraulic coupling included; but in this case, when utilizing my invention, the hydraulic coupling would run Wide open, that is, at full speed, performing no speed varying functions. I, of course, do not want to exclude the possibility of incorporating a hydraulic coupling between turbine 2 and pump 5, if there are such other reasons for having one.

It is of course intended to cover by the appended claims all such modifications and substitutions of equivalents as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. In a steam turbine powerplant including a turbine connected to drive a load device and supplied with steam from a boiler, the combination of:

a rst boiler feed pump driven at substantially constant speed and connected to supply to the boiler up to a preselected fraction of the feedwater required at full load,

feedwater valve means for regulating the flow to the boiler from the first pump,

a second boiler feed pump connected to supply to the boiler the balance of the feedwater required at full load,

a variable speed prime mover connected to drive said second pump,

and feedwater control means connected to control the speed of the variable speed prime mover when the demand for feedwater is above said preselected fraction of full load value and to regulate said feedwater valve means when the demand for feedwater is below said preselected fraction.

2. In a steam turbine powerplant having a main steam turbine connected to drive a load device at constant speed and supplied with steam from a main boiler, the combination of:

a first boiler feed pump connected to be driven at constant speed by the main turbine and to deliver to the boiler up to a preselected fraction of the feedwater required at full load,

valve means for controlling the flow of feedwater to the boiler from the first pump,

a second boiler feed pump connected to deliver to the boiler the balance of the feedwater required at full load,

a variable speed auxiliary steam turbine connected to drive said second pump, A

and feedwater control means connected t0 vary the speed of the auxiliary turbine when the demand for feedwater is above said preselected fraction of full load value, and to regulate said feedwater control valve means when the demand for feedwater is below said pre-selected fraction.

3. A steam turbine powerplant in accordance with claim 2 and including an auxiliary source of steam connected to supply motive lluid to the auxiliary turbine for starting the powerplant.

4. A steam turbine powerplant in accordance with claim 2 and including an auxiliary steam source connected to supply motive fluid to start the main turbine when the second boiler feed pump is out of service.

5. A steam turbine powerplant in accordance with claim 2 and including conduit means for supplying steam from varying the speed of the auxiliary turbine to vary the the main boiler to the auxiliary turbine. feedwater supply from the second pump from full 6. The method of operating a steam turbine powerplant load down to a preselected fraction of full load, and having a boiler supplying steam to a main turbine conregulating the flow -iof feedwater from the first pump nected to drive `at constant speed -both a load device and 5 to the boiler below said preselected fraction of full a rst pump supplying feedwater to the boiler, and a variload. able speed auxiliary steam turbine connected to drive a second pump supplying feedwater to the boiler, said meth- No references cited.

od including the steps of:

supplying feedwater from both pumps to the boiler at l0 EDGAR W. GEOGHEGAN, Przmary Exmmer.

full load, 

1. IN A STEAM TURBINE POWERPLANT INCLUDING A TURBINE CONNECTED TO DRIVE A LOAD DEVICE AND SUPPLIED WITH STEAM FROM A BOILER, THE COMBINATION OF: A FIRST BOILER FEED PUMP DRIVEN AT SUBSTANTIALLY CONSTANT SPEED AND CONNECTED TO SUPPLY TO THE BOILER UP TO A PRESELECTED FRACTION OF THE FEEDWATER REQUIRED AT FULL LOAD, FEEDWATER VALVE MEANS FOR REGULATING THE FLOW OF THE BOILER FROM THE FIRST PUMP, A SECOND BOILER FEED PUMP CONNECTED TO SUPPLY TO THE BOILER THE BALANCE OF THE FEEDWATER REQUIRED AT FULL LOAD, A VARIABLE SPEED PRIME MOVER CONNECTED TO DRIVE SAID SECOND PUMP, AND FEEDWATER CONTROL MEANS CONNECTED TO CONTROL THE SPEED OF THE VARIABLE SPEED PRIME MOVER WHEN THE DEMAND FOR FEEDWATER IS ABOVE SAID PRESELECTED FRACTION OF FULL LOAD VALUE AND TO REGULATE SAID FEEDWATER VALVE MEANS WHEN THE DEMAND FOR FEEDWATER IS BELOW SAID PRESELECTED FRACTION. 